When a child process exits, it sends exit_signal to its parent via do_notify_parent(). The clone() syscall constructs exit_signal as: (lower_32_bits(clone_flags) & CSIGNAL) CSIGNAL is 0xff, so values in the range 65-255 are possible. However, valid_signal() only accepts signals up to _NSIG (64 on x86_64), causing a WARN_ON in do_notify_parent() when the process exits: WARNING: kernel/signal.c:2174 do_notify_parent+0xc7e/0xd70 The syzkaller reproducer triggers this by calling clone() with flags=0x80, resulting in exit_signal = (0x80 & CSIGNAL) = 128, which exceeds _NSIG and is not a valid signal. The v1 of this patch added the check only in the clone() syscall handler, which is incomplete. kernel_clone() has other callers such as sys_ia32_clone() which would remain unprotected. Move the check to kernel_clone() to cover all callers. clone3() already validates exit_signal in copy_clone_args_from_user(). The comment above kernel_clone() states that callers are expected to validate exit_signal, but several callers never did. Adding the check to kernel_clone() enforces this for all callers centrally. Note that this is a user-visible change: previously, passing an invalid exit_signal to clone() was silently accepted. The man page for clone() does not document any defined behavior for invalid exit_signal values, so rejecting them with -EINVAL is the correct behavior. It is unlikely that any sane application relies on passing an invalid exit_signal. Reported-by: syzbot+bbe6b99feefc3a0842de@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=bbe6b99feefc3a0842de Tested-by: syzbot+bbe6b99feefc3a0842de@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/20260307064202.353405-1-kartikey406@gmail.com/T/ [v1] Fixes: 3f2c788a1314 ("fork: prevent accidental access to clone3 features") Signed-off-by: Deepanshu Kartikey --- kernel/fork.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index 947a8dbce06a..89d7eb67baf5 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2687,6 +2687,8 @@ pid_t kernel_clone(struct kernel_clone_args *args) (args->pidfd == args->parent_tid)) return -EINVAL; + if (!valid_signal(args->exit_signal)) + return -EINVAL; /* * Determine whether and which event to report to ptracer. When * called from kernel_thread or CLONE_UNTRACED is explicitly -- 2.43.0